Single-cell analysis of the mitogen-induced calcium responses of normal and protein kinase C-depleted Swiss 3T3 cells.

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Abstract
Single-cell fluorescence image analysis has been used to characterize the mitogen-induced increases in intracelluar free [Ca2+] ([Ca2+]i) in control and protein kinase C-depleted Swiss 3T3 cells. More than 80% of the control cells exhibited fast, transient response to bombesin, vasopressin, or prostaglandin F27a (PGF2.alpha.). In contrast, the [Ca2+]i responses induced by platelet-derived growth factor (PDGF) were markedly more heterogeneous, slower and often biphasic, with fewer cells (60-70%) responding. The peak [Ca2+]i values obtained in response to each mitogen showed substantial variation between cells. Brief pretreatment of the cells with 12-O-tetradecanoyl phorbol 13-acetate (TPA) reduced the [Ca2+]i responses to bombesin, but did not affect the responses to PDGF. Long-term pretreatment of the cells with TPA to down-modulate protein kinase C resulted in substantially prolonged [Ca2+]i responses to bombesin, vasopressin, and PGF2.alpha., but had no such effect on the responses to PDGF. We conclude that differences between the [Ca2+]i responses to bombesin and PDGF, previously reported using cell populations, reflect differences occurring in individual cells, and that the [Ca2+]i responses to bombesin, vasopressin, and PGF2.alpha. (but not PDGF) are subject to feedback inhibition via protein kinase C.

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