Ca2+-channel current and its modification by the dihydropyridine agonist BAY k 8644 in isolated smooth muscle cells
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The finding of resting potentials between −45 and −50 mV and the occurrence of spontaneous electrical activity when K+ was the predominant intracellular cation indicated that the cells were not leaky or hyperpermeable.
The existence of an inward Ca2+ current overlapping in time with an outward rectifying K+ current was demonstrated. The latter could be selectively blocked by replacing internal K+ with Cs+ and external Ca2+ with Ba2+.
Depolarizations to potentials between −40 and +50 mV evoked time-dependent inward currents, with a maximum peak value between −20 and 0 mV. For depolarizations beyond +50 mV time-dependent outward currents appeared. These currents were inhibited by 0.1 mM CdCl2.
The activation of the inward current showed a sigmoidal time course, and the rate of onset of the current increased at more positive potentials. Inactivation could be described by two exponentials.
The threshold for activation was about −40 mV, and full activation was reached at 0 mV. Inactivation was complete near 0 mV, whereas the channels were fully available at −80 mV.
The fully-activated Ca2+-channel current was strongly voltage dependent. The conductance decreased for potentials close to the reversal potential, and showed rectification for hyperpolarizing potentials.
The Ca2+ agonist BAY k 8644 enhanced the Ca2+-channel current without a significant effect on its kinetics. The fully-activated current and the steady-state activation were enhanced in a rather voltage-independent way.
Key wordsSmooth muscle Whole-cell patch clamp Ca2+ channels Ca2+ agonists
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- Barham RH, Drane W (1972) An algorithm for least squares estimation of nonlinear parameters when some of the parameters are linear. Technometrics 14:757–766Google Scholar
- Bolton TB, Tomita T, Vassort G (1981) Voltage clamp and measurement of ionic conductance in smooth muscle. In: Bulbring E, Brading AF, Jones AW, Tomita T (eds) Smooth muscle: an assessment of current knowledge, Chap. 2. Edward Arnold, LondonGoogle Scholar
- Brehm P, Eckert R (1978) Calcium entry leads to inactivation of calcium channel in paramecium. Science 202:1203–1205Google Scholar
- Brown AM, Kunze DL, Yatani A (1984) The agonist effect of dihydropyridines on Ca channels. Nature 311:570–572Google Scholar
- Byerly L, Hagiwara S (1982) Calcium currents in internally perfused nerve cell bodies ofLimnea stagnalis. J Physiol (Lond) 322: 503–528Google Scholar
- Callewaert G, Droogmans G (1986) Transient inward current through Ca channels in isolated smooth muscle cells. Effect of the dihydropyridine agonist BAY k 8644. Arch Int Pharmacodyn TherGoogle Scholar
- Cavalié A, Ochi R, Pelzer D, Trautwein W (1983) Elementary currents through Ca2+ channels in guinea-pig myocytes. Pflügers Arch 398:284–297Google Scholar
- Droogmans G, Callewaert G, Casteels R (1985) Single channel currents and whole-cell recording from isolated smooth muscle cells of the guinea-pig ileum. Arch Int Pharmacodyn Ther 227:330Google Scholar
- Eckert R, Chad JE (1984) Inactivation of Ca channels. Prog Biophys Mol Biol 44:215–267Google Scholar
- Fenwick EM, Marty A, Neher E (1982) Sodium and calcium channels in bovine chromaffin cells. J Physiol 331:599–635Google Scholar
- Fox AP (1981) Voltage-dependent inactivation of a calcium channel. Proc Natl Acad Sci USA 78:953–956Google Scholar
- Fukushima Y, Hagiwara S (1983) Voltage-gated Ca2+ channel in mouse myeloma cells. Proc Natl Acad Sci USA 80:2240–2242Google Scholar
- Hagiwara S, Byerly L (1981) Calcium channel. Annu Rev Neurosci 4:69–125Google Scholar
- Hagiwara S, Ohmori H (1982) Studies of calcium channels in rat clonal pituitary cells with patch electrode voltage clamp. J Physiol 331:231–252Google Scholar
- Hamill OP, Marty A, Neher E, Sakmann B, Sigworth FJ (1981) Improved patch-clamp techniques for high resolution current recording from cells and cell free membrane patches. Pflügers Arch 391:85–100Google Scholar
- Hess P, Lansman JB, Tsien RW (1984) Different modes of Ca channel gating behaviour favoured by dihydropyridine Ca agonists and antagonist. Nature 311:538–544Google Scholar
- Hess P, Tsien RW (1984) Mechanism of ion permeation through calcium channels. Nature 309:453–456Google Scholar
- Isenberg G, Klöckner U (1982) Calcium currents of isolated bovine ventricular myocytes are fast and of large amplitude. Pflügers Arch 395:30–41Google Scholar
- Kokubun S, Reuter H (1984) Dihydropyridine derivatives prolong the open state of Ca channels in cultured cardiac cells. Proc Natl Acad Sci USA 81:4824–4827Google Scholar
- Lee KS, Tsien RW (1984) High selectivity of calcium channels in single dialysed heart cells of the guinea-pig. J Physiol 354: 253–272Google Scholar
- Llinas R, Steinberg IZ, Walton K (1981) Presynaptic calcium currents in squid giant synapse. Biophys J 33:289–322Google Scholar
- Noma A, Kotake H, Kokubun S, Irisawa H (1981) Kinetics and rectification of the slow inward current in the rabbit sinoatrial node cell. Jpn J Physiol 31:491–500Google Scholar
- Schramm M, Thomas G, Towart R, Franckowiak G (1983) Novel dihydropyridines with positive inotropic action through activation of Ca2+ channels. Nature 303:535–537Google Scholar
- Sigworth FJ (1983) Electronic design of the patch clamp. In: Sakmann B, Neher E (eds) Single-channel recording, Chap. 1. Plenum Press, New YorkGoogle Scholar
- Thomas G, Chung M, Cohen CJ (1985) A dihydropyridine (BAY k 8644) that enhances calcium currents in guinea pig and calf myocardial cells. A new type of positive inotropic agent. Circ Res 56:87–96Google Scholar
- Tillotson D (1979) Inactivation of Ca conductance dependent on entry of Ca ions in molluscan neurons. Proc Natl Acad Sci USA 76:1497–1500Google Scholar
- Tsien RW (1983) Calcium channels in excitable cell membranes. Annu Rev Physiol 45:341–358Google Scholar
- Van Cauwenberghe S, Samijn D, Vereecke J, Verdonck F (1982) A flexible, low-cost microprocessor-based timer-stimulator. Arch Int Physiol Biochim 90:81–82Google Scholar
- Walsh JV, Singer JJ (1981) Voltage clamp of single freshly dissociated smooth muscle cells: current-voltage relationships for three currents. Pflügers Arch 390:207–210Google Scholar