Analysis of the store-dependent Ca entry mechanisms in adrenal chromaffin cells

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In this project, I analyzed membrane currents, intracellular Ca concentration ([Ca2+]i) and catecholamine (CA) secretion from isolated adrenal chromaffin cells to identify the functional roles of internal Ca stores and the store-dependent Ca entry mechanisms. A simultaneous on-line system for measurement of CA and ATP was made using culture cells. 1) In voltage-clamped chromaffin cells, Ca released from internal stores produced a transient [Ca2+]i increase concomitant with a transient outward K current. 2) In Ca-free conditions, [Ca2+]i increases derived from internal stores were abolished by inhibitors of Ca-ATPase and the elevation of [Ca2+]i was occurred after the re-application of external Ca. 3) CA secretion was elicited by Ca released from internal stores in single voltage-clamped cells. 4) The molar ratio of CA to ATP was constant regardless of secretagogues used. 5) Tyrosine kinase inhibitors suppressed the store-dependent Ca entry in smooth muscle cells. 6) Non-selective cation channel blockers and La inhibited Ca entry but in a different manner each other. It was revealed that internal Ca stores play functional roles in many cellular responses, including the regulation of ionic channels, change in [Ca2+]i and exocytosis. Store-dependent Ca entry may be partly mediated by tyrosine kinases. Further research is needed to identify the functional molecules such as trp-gene products, responsible for the store-dependent Ca entry mechanisms.