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  • Title: Dependence of Ca2+ channel currents on endogenous and exogenous sources of ATP in portal vein smooth muscle.
    Author: Lorenz JN, Paul RJ.
    Journal: Am J Physiol; 1997 Feb; 272(2 Pt 2):H987-94. PubMed ID: 9124463.
    Abstract:
    Metabolic pathways in vascular smooth muscles (VSM) appear to be functionally compartmentalized such that glycolysis fuels membrane-related processes, whereas oxidative processes fuel actin-myosin interaction. Because ATP influences Ca2+ channel activity, we examined the effects of ATP and metabolic substrates on Ca2+ channel activity with patch-clamp techniques in VSM cells isolated from rat portal vein. The peak magnitude of the Ca2+ channel currents was found to depend on the ATP concentration in the patch pipette. Cells perfused with 1, 3, and 5 mMATP had mean peak currents of 4.7 +/- 0.6, 12.2 +/- 1.9, and 17.6 +/- 2.0 pA/pF, respectively, and all currents showed substantial rundown. In separate experiments performed in the absence of intracellular ATP, provision of glycolytic but not oxidative substrates was able to maintain Ca2+ channel currents at levels comparable with those seen in the presence of 1 mM ATP. In the presence of 5 mM ATP, provision of glycolytic substrates resulted in a high peak current amplitude that was also very stable. Finally, metabolic inhibition with cyanide and iodoacetate caused a significant increase in the rate of current rundown, even in the presence of 5 mM ATP. These findings indicate that Ca2+ channel current is strongly dependent on ATP and that the source of ATP can also be an important factor. Compared with exogenous provision of ATP, endogenous metabolism preferentially maintained Ca2+ channel currents, consistent with the hypothesis of a functionally separate subsarcolemmal compartment. This provides an effective pathway for linking E-C coupling and vascular contractility to the metabolic state of the vascular cell.
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