Summary
The function of several key sarcolemmal proteins is modulated through phosphorylation-dephosphorylation of serine/threonine residues. While the involvement of sarcolemma-associated protein kinases in the phosphorylation of these proteins has been established, the nature of the protein phosphatases controlling these proteins has not been investigated. Rat heart sarcolemma contains two protein phosphatase isozymes, protein phosphatase 1 and 2A, which are distinguished on the basis of their susceptibility of inhibitor 2. Both isozymes elute from a Bio Gel A-0.5 column in association with the highest molecular weight protein fraction. However, some protein phosphatase 1 activity elutes with a smaller molecular weight fraction of about 37000, suggesting that the native enzyme exists as a catalytic subunit in complex with an anchor protein. Inhibition of the protein phosphatases using standard inhibitors leads to a stimulation in both the rate and extent of32P incorporation into isolated sarcolemma. Also affected by inhibition of protein phosphatase activity is the rate of ATP-dependent calcium uptake, which is stimulated following exposure to either inhibitor 2, a classical protein phosphatase 1 inhibitor, and microcystin, a protein phosphatase 1 and 2A inhibitor. The data suggest that the protein phosphatases regulate the dephosphorylation of sarcolemmal proteins Through this mechanism they serve as important modulators of the sarcolemmal Ca2+ pump.
Similar content being viewed by others
References
Allo SN, Schaffer SW (1990) Defective sarcolemmal phosphorylation associated with noninsulin-dependent diabetes. Biochim Biophys Acta 1023:206–212
Caroni P, Carafoli E (1981) Regulation of Ca2+-pumping ATPase of heart sarcolemma by a phosphorylation-dephosphorylation process. J Biol Chem 256:9371–9373
Chisholm AAK, Cohen P (1988) The myosin-bound form of protein phosphatase 1 (PP-1M) is the enzyme that dephosphorylates native myosin in skeletal and cardiac muscles. Biochim Biophys Acta 971:163–169
Cohen P, Cohen PTW (1989) Protein phosphatases come of age. J Biol Chem 264:21435–21438
Dent P, Lavoinne A, Nakielny S, Caudwell FB, Watt P, Cohen P (1990) The molecular mechanism by which insulin stimulates glycogen synthesis in mammalian skeletal muscle. Nature 348:1–6
Ganguly PK, Pierce GN, Dhalla KS, Dhalla NS (1983) Defective sarcoplasmic reticular calcium transport in diabetic cardiomyopathy. Am J Physiol 244:E528-E535
Heyliger CE, Prakash A, McNeill JH (1987) Alterations in cardiac sarcolemmal Ca2+ pump activity during diabetes mellitus. Am J Physiol 252:H540-H544
Ingebritsen TS, Stewart AA, Cohen P (1983) The protein phosphatases involved in cellular regulation: 6a. Measurement of type-1 and type-2 protein phosphatases in extracts of mammalian tissues; an assessment of their physiological roles. Eur J Biochem 132:297–307
Katz AM, Repke DI, Upshaw JE, Polascik MA (1970) Characterization of dog cardiac microsomes: use of zonal centrifugation to fractionate fragmented sarcoplasmic reticulum, (Na+, K+) activated ATPase and mitochondrial fragments. Biochim Biophys Acta 205:473–490
Lamers, JMJ (1985) Calcium transport systems in cardiac sarcolemma and their regulation by the second messengers cyclic AMP and calcium-calmodulin. Gen Physiol Biophys 4:143–154
Lamers JMJ, Stinis HT, DeJonge HR (1981) On the role of cyclic AMP and Ca2+-calmodulin-dependent phosphorylation in the control of (Ca2++Mg2+)-ATPase of cardiac sarcolemma. FEBS Lett 127:139–143
MacDougall LK, Jones LR, Cohen P (1991) Identification of the major protein phosphatases in mammalian cardiac muscle which dephosphorylate phospholamban. Eur J Biochem 196:725–734
Makino N, Dhalla KS, Elimban V, Dhalla NS (1987) Sarcolemmal Ca2+ transport in streptozotocin-induced diabetic cardiomyopathy in rats. Am J Physiol 253:E202-E207
Neumann J, Gupta RC, Schmitz W, Scholz H, Nairn AC, Watanabe AM (1991) Evidence for isoproterenol-induced phosphorylation of phosphatase inhibitor-1 in the intact heart. Circ Res 69:1450–1457
Pitts, BJR (1979) Stoichiometry of sodium-calcium exchange in cardiac sarcolemmal vesicles. J Biol Chem 254:6232–6235
Schaffer SW, Allo S, Punna S, White T (1991) Defective response to cAMP-dependent protein kinase in non-insulin-dependent diabetic heart. Am J Physiol 261:E369-E376
Schlender KK, Wang W, Wilson SE (1989) Evidence for a latent form of protein phosphatase 1. Biochem Biophys Res Commun 159:72–78
Tang PM, Bondor JA, Swiderek KM, DePaoli-Roach AA (1991) Molecular cloning and expression of the regulatory (RG1) subunit of the glycogen-associated protein phosphatase. J Biol Chem 266:15782–15789
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Schaffer, S.W., Punna, S. Regulation of sarcolemmal Ca2+ pump by endogenous protein phosphatases. Basic Res Cardiol 88, 103–110 (1993). https://doi.org/10.1007/BF00798258
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00798258