Abstract
The cerebrospinal fluid (CSF) provides mechanical and chemical protection of the brain and spinal cord. This review focusses on the contribution of the choroid plexus epithelium to the water and salt homeostasis of the CSF, i.e. the secretory processes involved in CSF formation. The choroid plexus epithelium is situated in the ventricular system and is believed to be the major site of CSF production. Numerous studies have identified transport processes involved in this secretion, and recently, the underlying molecular background for some of the mechanisms have emerged. The nascent CSF consists mainly of NaCl and NaHCO3, and the production rate is strictly coupled to the rate of Na+ secretion. In contrast to other secreting epithelia, Na+ is actively pumped across the luminal surface by the Na+,K+-ATPase with possible contributions by other Na+ transporters, e.g. the luminal Na+,K+,2Cl− cotransporter. The Cl− and HCO3 − ions are likely transported by a luminal cAMP activated inward rectified anion conductance, although the responsible proteins have not been identified. Whereas Cl− most likely enters the cells through anion exchange, the functional as well as the molecular basis for the basolateral Na+ entry are not yet well-defined. Water molecules follow across the epithelium mainly through the water channel, AQP1, driven by the created ionic gradient. In this article, the implications of the recent findings for the current model of CSF secretion are discussed. Finally, the clinical implications and the prospects of future advances in understanding CSF production are briefly outlined.
Similar content being viewed by others
References
Alper SL, Stuart-Tilley A, Simmons CF, Brown D, Drenckhahn D (1994) The fodrin-ankyrin cytoskeleton of choroid plexus preferentially colocalizes with apical Na+K(+)-ATPase rather than with basolateral anion exchanger AE2. J Clin Invest 93:1430–1438
Alper SL, Stuart-Tilley AK, Biemesderfer D, Shmukler BE, Brown D (1997) Immunolocalization of AE2 anion exchanger in rat kidney. Am J Physiol 273:F601–F614
Ames A III, Higashi K, Nesbett FB (1965) Relation of potassium concentration in choroid plexus fluid to that in plasma. J Physiol 181:506–515
Ames A III, Higashi K, Nesbett FB (1965) Effects of Pco2 acetazolamide and ouabain on volume and composition of choroid-plexus fluid. J Physiol 181:516–524
Ames A III, Sakanoue M, Endo S (1964) Na, K, Ca, Mg, and Cl concentrations in choroid plexus fluid and cisternal fluid compared with plasma ultrafiltrate. J Neurophysiol 27:672–681
Amin MS, Wang HW, Reza E, Whitman SC, Tuana BS, Leenen FH (2005) Distribution of epithelial sodium channels and mineralocorticoid receptors in cardiovascular regulatory centers in rat brain. Am J Physiol Regul Integr Comp Physiol 289:R1787–R1797
Bairamian D, Johanson CE, Parmelee JT, Epstein MH (1991) Potassium cotransport with sodium and chloride in the choroid plexus. J Neurochem 56:1623–1629
Battle T, Preisser L, Marteau V, Meduri G, Lambert M, Nitschke R, Brown PD, Corman B (2000) Vasopressin V1a receptor signaling in a rat choroid plexus cell line. Biochem Biophys Res Commun 275:322–327
Bouzinova EV, Praetorius J, Virkki LV, Nielsen S, Boron WF, Aalkjaer C (2005) Na+-dependent HCO3 − uptake into the rat choroid plexus epithelium is partially DIDS sensitive. Am J Physiol Cell Physiol 289:C1448–C1456
Brown PD, Davies SL, Speake T, Millar ID (2004) Molecular mechanisms of cerebrospinal fluid production. Neuroscience 129:957–970
Brown PD, Pakhomova A, Millar ID (2006) NKCC1 does not contribute to volume regulation in epithelial cells isolated from mouse choroid plexus. Proc Physiol Soc 2:PC15 (Abstract)
Burg MB, Orloff J (1968) Control of fluid absorption in the renal proximal tubule. J Clin Invest 47:2016–2024
Chodobski A, Loh YP, Corsetti S, Szmydynger-Chodobska J, Johanson CE, Lim YP, Monfils PR (1997) The presence of arginine vasopressin and its mRNA in rat choroid plexus epithelium. Brain Res Mol Brain Res 48:67–72
Chodobski A, Summy-Long J, Lin MWS, Wojcik BE, Bui V, Kil E, Johanson CE (2000) Regulation of choroidal vasopressin secretion by the cAMP/PKA signalling patheway and the possible autocrine actions. Soc Neurosci Abstr 26:337 (Abstract)
Chodobski A, Szmydynger-Chodobska J (2001) Choroid plexus: target for polypeptides and site of their synthesis. Microsc Res Tech 52:65–82
Chodobski A, Szmydynger-Chodobska J, Johanson CE (1998) Vasopressin mediates the inhibitory effect of central angiotensin II on cerebrospinal fluid formation. Eur J Pharmacol 347:205–209
Chodobski A, Szmydynger-Chodobska J, Vannorsdall MD, Epstein MH, Johanson CE (1994) AT1 receptor subtype mediates the inhibitory effect of central angiotensin II on cerebrospinal fluid formation in the rat. Regul Pept 53:123–129
Chodobski A, Wojcik BE, Loh YP, Dodd KA, Szmydynger-Chodobska J, Johanson CE, Demers DM, Chun ZG, Limthong NP (1998) Vasopressin gene expression in rat choroid plexus. Adv Exp Med Biol 449:59–65
Christensen O, Zeuthen T (1987) Maxi K+ channels in leaky epithelia are regulated by intracellular Ca2+, pH and membrane potential. Pflugers Arch 408:249–259
Cornford EM, Varesi JB, Hyman S, Daiman RT, Raleigh MJ (1997) Mitochondrial content of choroid plexus epithelium. Exp Brain Res 399–405
Crook RB, Farber MB, Prusiner SB (1984) Hormones and neurotransmitters control cyclic AMP metabolism in choroid plexus epithelial cells. J Neurochem 42:340–350
Csaky TZ, Rigor BM (1967) The choroid plexus as a glucose barrier. In: Lajtha A, Ford DH (eds) Progress in brain research. Elsevier, Amsterdam, pp 147–158
Cserr HF (1971) Physiology of the choroid plexus. Physiol Rev 51:273–311
Cushing H (1914) Studies on the cerebrospinal fluid. J Med Res 26:1–19
Davson H, Segal MB (1996) Physiology of the CSF and blood–brain barriers. CRC Press, Boca Raton
Davson H, Kleeman CR, Levin E (1962) Quantitative studies of the passage of different substances out of the cerebrospinal fluid. J Physiol 161:126–142
Davson H, Purvis C (1954) Cryoscopic apparatus suitable for studies on aqueous humour and cerebro-spinal fluid. J Physiol 124:12P–13P
Davson H, Segal MB (1970) The effects of some inhibitors and accelerators of sodium transport on the turnover of 22Na in the cerebrospinal fluid and the brain. J Physiol 209:131–153
Deng QS, Johanson CE (1989) Stilbenes inhibit exchange of chloride between blood, choroid plexus and cerebrospinal fluid. Brain Res 501:183–187
Deng QS, Johanson CE (1992) Cyclic AMP alteration of chloride transport into the choroid plexus–cerebrospinal fluid system. Neurosci Lett 143:146–150
Doring F, Derst C, Wischmeyer E, Karschin C, Schneggenburger R, Daut J, Karschin A (1998) The epithelial inward rectifier channel Kir7.1 displays unusual K+ permeation properties. J Neurosci 18:8625–8636
Emerich DF, Skinner SJ, Borlongan CV, Vasconcellos AV, Thanos CG (2005) The choroid plexus in the rise, fall and repair of the brain. Bioessays 27:262–274
Faivre J (1854) Structure du conarium et des plexus choroïde chez l’hommes et des animaux. Gaz Med Paris 9:555–556
Faraci FM, Mayhan WG, Heistad DD (1990) Effect of vasopressin on production of cerebrospinal fluid: possible role of vasopressin (V1)-receptors. Am J Physiol 258:R94–R98
Fencl V, Vale JR, Broch JA (1969) Respiration and cerebral blood flow in metabolic acidosis and alkalosis in humans. J Appl Physiol 27:67–76
Fenton RA, Flynn A, Shodeinde A, Smith CP, Schnermann J, Knepper MA (2005) Renal phenotype of UT-A urea transporter knockout mice. J Am Soc Nephrol 16:1583–1592
Feschenko MS, Donnet C, Wetzel RK, Asinovski NK, Jones LR, Sweadner KJ (2003) Phospholemman, a single-span membrane protein, is an accessory protein of Na,K-ATPase in cerebellum and choroid plexus. J Neurosci 23:2161–2169
Halmi P, Parkkila S, Honkaniemi J (2006) Expression of carbonic anhydrases II, IV, VII, VIII and XII in rat brain after kainic acid induced status epilepticus. Neurochem Int 48:24–30
Haselbach M, Wegener J, Decker S, Engelbertz C, Galla HJ (2001) Porcine choroid plexus epithelial cells in culture: regulation of barrier properties and transport processes. Microsc Res Tech 52:137–152
Heisey SR, Held D, Pappenheimer JR (1962) Bulk flow and diffusion in the cerebrospinal fluid system of the goat. Am J Physiol 203:775–781
Held D, Fencl V, Pappenheimer JR (1964) Electrical potential of cerebrospinal fluid. J Neurophysiol 27:942–959
Javaheri S, Wagner KR (1993) Bumetanide decreases canine cerebrospinal fluid production. In vivo evidence for NaCl cotransport in the central nervous system. J Clin Invest 92:2257–2261
Johanson C, McMillan P, Tavares R, Spangenberger A, Duncan J, Silverberg G, Stopa E (2004) Homeostatic capabilities of the choroid plexus epithelium in Alzheimer’s disease. Cerebrospinal Fluid Res 1:1–16
Johanson CE, Murphy VA (1990) Acetazolamide and insulin alter choroid plexus epithelial cell [Na+], pH, and volume. Am J Physiol 258:F1538–F1546
Johanson CE, Preston JE, Chodobski A, Stopa EG, Szmydynger-Chodobska J, McMillan PN (1999) AVP V1 receptor-mediated decrease in Cl− efflux and increase in dark cell number in choroid plexus epithelium. Am J Physiol 276:C82–C90
Johnston M, Zakharov A, Papaiconomou C, Salmasi G, Armstrong D (2004) Evidence of connections between cerebrospinal fluid and nasal lymphatic vessels in humans, non-human primates and other mammalian species. Cerebrospinal Fluid Research 1:2 DOI 10.1186/1743-8454-1-2
Kajita H, Brown PD (1997) Inhibition of the inward-rectifying Cl− channel in rat choroid plexus by a decrease in extracellular pH. J Physiol 498 (Pt 3):703–707
Kalaria RN, Premkumar DR, Lin CW, Kroon SN, Bae JY, Sayre LM, LaManna JC (1998) Identification and expression of the Na+/H+ exchanger in mammalian cerebrovascular and choroidal tissues: characterization by amiloride-sensitive [3H]MIA binding and RT-PCR analysis. Brain Res Mol Brain Res 58:178–187
Kallio H, Pastorekova S, Pastorek J, Waheed A, Sly WS, Mannisto S, Heikinheimo M, Parkkila S (2006) Expression of carbonic anhydrases IX and XII during mouse embryonic development. BMC Dev Biol 6:22 (Epub ahead of print)
Kanaka C, Ohno K, Okabe A, Kuriyama K, Itoh T, Fukuda A, Sato K (2001) The differential expression patterns of messenger RNAs encoding K–Cl cotransporters (KCC1,2) and Na–K–2Cl cotransporter (NKCC1) in the rat nervous system. Neuroscience 104:933–946
Kazemi H, Johnson DC (1986) Regulation of cerebrospinal fluid acid–base balance. Physiol Rev 66:953–1037
Keep RF, Jones HC (1990) A morphometric study on the development of the lateral ventricle choroid plexus, choroid plexus capillaries and ventricular ependyma in the rat. Brain Res Dev Brain Res 56:47–53
Keep RF, Xiang J, Betz AL (1994) Potassium cotransport at the rat choroid plexus. Am J Physiol 267:C1616–C1622
Kibble JD, Garner C, Colledge WH, Brown S, Kajita H, Evans M, Brown PD (1997) Whole cell Cl− conductances in mouse choroid plexus epithelial cells do not require CFTR expression. Am J Physiol 272:C1899–C1907
Kibble JD, Trezise AE, Brown PD (1996) Properties of the cAMP-activated C1—current in choroid plexus epithelial cells isolated from the rat. J Physiol 496 (Pt 1):69–80
Kotera T, Brown PD (1994) Evidence for two types of potassium current in rat choroid plexus epithelial cells. Pflugers Arch 427:317–324
Li H, Tornberg J, Kaila K, Airaksinen MS, Rivera C (2002) Patterns of cation-chloride cotransporter expression during embryonic rodent CNS development. Eur J Neurosci 16:2358–2370
Lindsey AE, Schneider K, Simmons DM, Baron R, Lee BS, Kopito RR (1990) Functional expression and subcellular localization of an anion exchanger cloned from choroid plexus. Proc Natl Acad Sci USA 87:5278–5282
Livingston RB (1949) Cerebrospinal fluid. In: Fulton JF (ed) A textbook of physiology. Saunders, Philadelphia, pp 916–980
Marrs JA, Napolitano EW, Murphy-Erdosh C, Mays RW, Reichardt LF, Nelson WJ (1993) Distinguishing roles of the membrane-cytoskeleton and cadherin mediated cell–cell adhesion in generating different Na+,K(+)-ATPase distributions in polarized epithelia. J Cell Biol 123:149–164
Masuzawa T, Ohta T, Kawamura M, Nakahara N, Sato F (1984) Immunohistochemical localization of Na+, K+-ATPase in the choroid plexus. Brain Res 302:357–362
Maurizi CP (2003) The puzzle of where cerebrospinal fluid is absorbed: new pieces. Med Hypotheses 60:102–103
Mayer SE, Sanders-Bush E (1993) Sodium-dependent antiporters in choroid plexus epithelial cultures from rabbit. J Neurochem 60:1308–1316
Melby JM, Miner LC, Reed DJ (1982) Effect of acetazolamide and furosemide on the production and composition of cerebrospinal fluid from the cat choroid plexus. Can J Physiol Pharm 60:405–409
Moon Y, Hong SJ, Shin D, Jung Y (2006) Increased aquaporin-1 expression in choroid plexus epithelium after systemic hyponatremia. Neurosci Lett 395:1–6
Morales-Mulia M, Pasantes-Morales H, Moran J (2000) Volume sensitive efflux of taurine in HEK293 cells overexpressing phospholemman. Biochim Biophys Acta 1496:252–260
Murphy VA, Johanson CE (1989) Alteration of sodium transport by the choroid plexus with amiloride. Biochim Biophys Acta 979:187–192
Murphy VA, Johanson CE (1989) Acidosis, acetazolamide, and amiloride: effects on 22Na transfer across the blood-brain and blood–CSF barriers. J Neurochem 52:1058–1063
Murphy VA, Johanson CE (1990) Na(+)-H+ exchange in choroid plexus and CSF in acute metabolic acidosis or alkalosis. Am J Physiol 258:F1528–F1537
Nakamura N, Suzuki Y, Sakuta H, Ookata K, Kawahara K, Hirose S (1999) Inwardly rectifying K+ channel Kir7.1 is highly expressed in thyroid follicular cells, intestinal epithelial cells and choroid plexus epithelial cells: implication for a functional coupling with Na+,K+-ATPase. Biochem J 342 (Pt 2):329–336
Netter FM (2003) Atlas der Anatomie des Menschen. 3rd ed. Thieme, Stuttgart
Nielsen S, Smith BL, Christensen EI, Agre P (1993) Distribution of the aquaporin CHIP in secretory and resorptive epithelia and capillary endothelia. Proc Natl Acad Sci USA 90:7275–7279
Nilsson C, Ekman R, Lindvall-Axelsson M, Owman C (1990) Distribution of peptidergic nerves in the choroid plexus, focusing on coexistence of neuropeptide Y, vasoactive intestinal polypeptide and peptide histidine isoleucine. Regul Pept 27:11–26
Oshio K, Song Y, Verkman AS, Manley GT (2003) Aquaporin-1 deletion reduces osmotic water permeability and cerebrospinal fluid production. Acta Neurochir Suppl 86:525–528
Oshio K, Watanabe H, Song Y, Verkman AS, Manley GT (2005) Reduced cerebrospinal fluid production and intracranial pressure in mice lacking choroid plexus water channel Aquaporin-1. FASEB J 19:76–78
Palmer CJ, Scott BT, Jones LR (1991) Purification and complete sequence determination of the major plasma membrane substrate for cAMP-dependent protein kinase and protein kinase C in myocardium. J Biol Chem 266:11126–11130
Patlak CS, Adamson RH, Oppelt WW, Rall DP (1966) Potential difference of the ventricular fluid in vivo and in vitro in the dogfish. Life Sci 5:2011–2015
Pearson MM, Lu J, Mount DB, Delpire E (2001) Localization of the K(+)-Cl(−) cotransporter, KCC3, in the central and peripheral nervous systems: expression in the choroid plexus, large neurons and white matter tracts. Neuroscience 103:481–491
Peters A, Palay SL, Webster HDF (1976) The fine structure of the nervous system. Saunders, Philadelphia
Phillips PA, Abrahams JM, Kelly J, Paxinos G, Grzonka Z, Mendelsohn FA, Johnston CI (1988) Localization of vasopressin binding sites in rat brain by in vitro autoradiography using a radioiodinated V1 receptor antagonist. Neuroscience 27:749–761
Plotkin MD, Kaplan MR, Peterson LN, Gullans SR, Hebert SC, Delpire E (1997) Expression of the Na(+)-K(+)-2Cl- cotransporter BSC2 in the nervous system. Am J Physiol 272:C173–C183
Pollay M, Curl F (1967) Secretion of cerebrospinal fluid by the ventricular ependyma of the rabbit. Am J Physiol 213:1031–1038
Pollay M, Stevens E, Estrada S, Kaplan R (1972) Extracorporal perfusion of choroid plexus. J Appl Physiol 32:612–617
Praetorius J, Bouzinova EV, Boron WF, Aalkjaer C, Nielsen S (2005) Expression of bicarbonate transporters and aquaporins in the choroid plexus. EB/IUPS 922.2 (Abstract)
Praetorius J, Nejsum LN, Nielsen S (2004) A SCL4A10 gene product maps selectively to the basolateral plasma membrane of choroid plexus epithelial cells. Am J Physiol Cell Physiol 286:C601–C610
Praetorius J, Nielsen S (2006) Distribution of sodium transporters and aquaporin-1 in the human choroid plexus. Am J Physiol Cell Physiol 291:C59–C67
Pushkin A, Abuladze N, Newman D, Lee I, Xu G, Kurtz I (2000) Cloning, characterization and chromosomal assignment of NBC4, a new member of the sodium bicarbonate cotransporter family. Biochim Biophys Acta 1493:215–218
Redzic ZB, Segal MB (2004) The structure of the choroid plexus and the physiology of the choroid plexus epithelium. Adv Drug Deliv Rev 56:1695–1716
de Rougemont J, Ames A III, Nesbett FB, Hofmann HF (1960) Fluid formed by choroid plexus; a technique for its collection and a comparison of its electrolyte composition with serum and cisternal fluids. J Neurophysiol 23:485–495
Royer P (1950) Perfusion of the cerebral spaces. Biol Med (Paris) 39:237–269
Sato O, Bering EA (1967) Extra-ventricular formation of cerebrospinal fluid. No To Shinkei 19:883–885
Schnermann J, Chou CL, Ma T, Traynor T, Knepper MA, Verkman AS (1998) Defective proximal tubular fluid reabsorption in transgenic aquaporin-1 null mice. Proc Natl Acad Sci USA 95:9660–9664
Segal MB (2001) Transport of nutrients across the choroid plexus. Microsc Res Tech 52:38–48
Segal MB, Burgess AM (1974) A combined physiological and morphological study of the secretory process in the rabbit choroid plexus. J Cell Sci 14:339–350
Serot JM, Bene MC, Faure GC (2003) Choroid plexus, aging of the brain, and Alzheimer’s disease. Front Biosci 8:s515–s521
Siegel GJ, Holm C, Schreiber JH, Desmond T, Ernst SA (1984) Purification of mouse brain (Na+ + K+)-ATPase catalytic unit, characterization of antiserum, and immunocytochemical localization in cerebellum, choroid plexus, and kidney. J Histochem Cytochem 32:1309–1318
Speake T, Freeman LJ, Brown PD (2003) Expression of aquaporin 1 and aquaporin 4 water channels in rat choroid plexus. Biochim Biophys Acta 1609:80–86
Speake T, Kajita H, Smith CP, Brown PD (2002) Inward-rectifying anion channels are expressed in the epithelial cells of choroid plexus isolated from ClC-2 ’knock-out’ mice. J Physiol 539:385–390
Speake T, Kibble JD, Brown PD (2004) Kv1.1 and Kv1.3 channels contribute to the delayed-rectifying K+ conductance in rat choroid plexus epithelial cells. Am J Physiol Cell Physiol 286:C611–C620
Speake T, Whitwell C, Kajita H, Majid A, Brown PD (2001) Mechanisms of CSF secretion by the choroid plexus. Microsc Res Tech 52:49–59
Sterling D, Alvarez BV, Casey JR (2002) The extracellular component of a transport metabolon. Extracellular loop 4 of the human AE1 Cl−/ HCO3 − exchanger binds carbonic anhydrase IV. J Biol Chem 277:25239–25246
Sterling D, Reithmeier RA, Casey JR (2001) A transport metabolon. Functional interaction of carbonic anhydrase II and chloride/bicarbonate exchangers. J Biol Chem 276:47886–47894
Virkki LV, Wilson DA, Vaughan-Jones RD, Boron WF (2002) Functional characterization of human NBC4 as an electrogenic Na+-HCO cotransporter (NBCe2). Am J Physiol Cell Physiol 282:C1278–C1289
Vogh BP, Godman DR, Maren TH (1987) Effect of AlCl3 and other acids on cerebrospinal fluid production: a correction. J Pharmacol Exp Ther 243:35–39
Vogh BP, Langham MR Jr. (1981) The effect of furosemide and bumetanide on cerebrospinal fluid formation. Brain Res 221:171–183
Wang CZ, Yano H, Nagashima K, Seino S (2000) The Na+-driven Cl−/HCO3 − exchanger. Cloning, tissue distribution, and functional characterization. J Biol Chem 275:35486–35490
Watts AG, Sanchez-Watts G, Emanuel JR, Levenson R (1991) Cell-specific expression of mRNAs encoding Na+,K(+)-ATPase alpha- and beta-subunit isoforms within the rat central nervous system. Proc Natl Acad Sci USA 88:7425–7429
Weaver CE, McMillan PN, Duncan JA, Stopa EG, Johanson CE (2003) Hydrocephalus disorders: their biophysical and neuroendocrine impact on the choroid plexus epithelium. Advances in Molecular and Cell Biology 31:269–293
Welch K (1963) Secretion of cerebrospinal fluid by choroid plexus of the rabbit. Am J Physiol 205:617–624
Welch K, Pollay M (1961) Perfusion of particles through arachnoid villi of the monkey. Am J Physiol 201:651–654
Wright EM (1978) Transport processes in the formation of the cerebrospinal fluid. Rev Physiol Biochem Pharmacol 83:3–34
Wright EM (1972) Mechanisms of ion transport across the choroid plexus. J Physiol 226:545–571
Wu Q, Delpire E, Hebert SC, Strange K (1998) Functional demonstration of Na+-K+-2Cl− cotransporter activity in isolated, polarized choroid plexus cells. Am J Physiol 275:C1565–C1572
Yang T, Huang YG, Singh I, Schnermann J, Briggs JP (1996) Localization of bumetanide- and thiazide-sensitive Na-K-Cl cotransporters along the rat nephron. Am J Physiol 271:F931–F939
Zeuthen T (1994) Cotransport of K+, Cl− and H2O by membrane proteins from choroid plexus epithelium of Necturus maculosus. J Physiol 478 (Pt 2):203–219
Zeuthen T, Wright EM (1981) Epithelial potassium transport: tracer and electrophysiological studies in choroid plexus. J Membr Biol 60:105–128
Zeuthen T, Wright EM (1978) An electrogenic NA+/K+ pump in the choroid plexus. Biochim Biophys Acta 511:517–522
Acknowledgement
Helle A. Praetorius and Robert A. Fenton are thanked for fruitful discussions and for valuable input regarding the manuscript.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Praetorius, J. Water and solute secretion by the choroid plexus. Pflugers Arch - Eur J Physiol 454, 1–18 (2007). https://doi.org/10.1007/s00424-006-0170-6
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00424-006-0170-6