CYTOSOLIC CA2+ OSCILLATIONS IN REF52 FIBROBLASTS - CA2+-STIMULATED IP3 PRODUCTION OR VOLTAGE-DEPENDENT CA2+ CHANNELS AS KEY POSITIVE FEEDBACK ELEMENTS

Oscillations in cytosolic free calcium concentrations ([Ca2+]i) can be elicited in REF52 fibroblasts by three different modes of stimulation. We have previously demonstrated that [Ca2+]i oscillations result when these cells are simulataneously depolarized and stimualted with a hormone linked to phosphoinositide breakdown. Further evidence is now presented that such oscillations are linked to fluctuations in the concentration of IP3 and the Ca2+ content of an IP3-sensitive Ca2+ store. [Ca2+]i oscillations can also be generated in REF52 cells either by direct stimulation of G-proteins with GTP-gamma-S or AIF4- or by destabilizing the membrane potential and opening voltage-dependent calcium channels. This report compares the different types of oscillations and their mechanisms.