Modulation of N-type calcium channels translocation in RINm5F insulinoma cells

An intracellular pool of N-type voltage-operated calcium channels has recen tly been described in both IMR32 human neuroblastoma and PC12 rat pheochrom ocytoma cells. These channels were found to be accumulated in subcellular f ractions where the chromogranin B-containing secretory granules were also e nriched. Upon exocytosis N-type calcium channels were: reversibly inserted in the plasma membrane. We have now extended this study to RINm5F rat insul inoma cells, and characterized the parallelism between the 'regulated' secr etion of serotonin and the recruitment of surface calcium channels. Exoctos is was stimulated by different means, such as depolarization with high KCI, high Ba2+ alone or protein kinase C activation; on the other hand exocytos is was inhibited with the non-selective calcium channel antagonist Cd2+ Or with noradrenaline. Stimulated release was always accompanied, with paralle l kinetics. by calcium channel recruitment, while inhibition of secretion b locked calcium channel recruitment too. During repetitive depolarizations w e revealed a potentiation of [Ca2+](i) transients in single Fura-2 loaded R INm5F cells, that was accompanied by an increase in surface VOCCs, suggesti ng a physiological role for the newly recruited channels. (C) 2000 Academic Press.