Muscarinic agonists activate Ca2+ store-operated and -independent ionic currents in insulin-secreting HIT-T15 cells and mouse pancreatic beta-cells.

Autor:	Mears, D., Zimliki, C. L.
Předmět:	ACETYLCHOLINE INSULIN PANCREATIC secretions CELLS IONS CALCIUM metabolism ANIMAL experimentation CALCIUM CARRIER proteins CELL culture CELL lines CELL receptors CELLULAR signal transduction COMPARATIVE studies DOSE-effect relationship in pharmacology HAMSTERS HEPARIN HYDROCARBONS ISLANDS of Langerhans ISLANDS of Langerhans tumors RESEARCH methodology MEDICAL cooperation MEMBRANE proteins MICE PARASYMPATHOMIMETIC agents PROTEINS RESEARCH EVALUATION research MUSCARINIC agonists CHEMICAL inhibitors PHARMACODYNAMICS
Zdroj:	Journal of Membrane Biology; Jan2004, Vol. 197 Issue 1, p59-70, 12p
Abstrakt:	The neurotransmitter acetylcholine, a muscarinic receptor agonist, augments glucose-induced insulin secretion from pancreatic β-cells by depolarizing the membrane to enhance voltage-gated Ca2+ influx. To clarify the electrical events involved in this process, we measured ionic currents from a clonal β-cell line (HIT-T15) and mouse pancreatic β-cells. In whole-cell recordings, the muscarinic agonist carbachol (CCh) dose-dependently and reversibly activated a voltage-independent, nonselective current (whole-cell conductance 24 pS/pF, reversal potential ~-15 mV). The current, which we refer to as Imusc, was blocked by atropine, a muscarinic receptor antagonist, and SKF 96365, a nonspecific ion channel blocker. The magnitude of the current decreased by 52% when extracellular Na+ was removed, but was not affected by changes in extracellular Ca2+, confirming that Imusc is a nonselective current. To determine if Imusc activates following release of Ca2+ from an intracellular store, we blocked intracellular IP3 receptors with heparin. Carbachol still activated a current in the presence of heparin, demonstrating the presence of a Ca2+ store-independent, muscarinic agonist-activated ionic current in HIT cells. However, the store-independent current was smaller and had a more positive reversal potential (~0 mV) than the current activated by CCh under control conditions. This result indicates that heparin had blocked a component of Imusc, which likely activates following release of stored Ca2+. Depleting IP3-sensitive calcium stores with thapsigargin also activated a non-selective, SKF 96365-blockable current in HIT cells. The properties of this putative store-operated current were similar to the component of Imusc that was blocked by heparin, being voltage-independent and reversing near -30 mV. We conclude that Imusc consists of store-operated and store-independent components, both of which may contribute to the depolarizing action of muscarinic agonists on pancreatic β-cells. [ABSTRACT FROM AUTHOR]
Databáze:	Complementary Index
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