Acetylcholine-induced calcium signaling in pancreatic beta-cells derived from protein kinase C epsilon deficient mice

Acetylcholine (ACH) increases cytosolic free calcium ([Ca2+]i) and insulin secretion from beta-cells. Several PKCs exist, which serve distinct functions. Previous studies showed that PKCs are involved in ACH-induced Ca2+ signaling and insulin secretion. It is unknown, whether PKCepsilon(e), that is activated upon ACH receptor stimulation, is involved in ACH-linked Ca2+ signaling.

Material and Methods: [Ca2+]i was measured in single fura-2 loaded beta-cells derived from PKCe–/– or wildtype(wt) mice.

Results: The ACH analogue carbachol (10µM) caused a biphasic rise in [Ca2+]i with an initial peak followed by a sustained plateau both in PKCe–/– and wt beta-cells. The initial peak, mainly reflecting mobilization of internal calcium, was similar in PKCe–/– beta-cells as compared to wt cells (Δ[Ca2+]i PKCe–/–110±9 nM (n=59) vs. Δ[Ca2+]i wt 134±9 nM (n=61, p=0,08)). The plateau-phase, which requires Ca2+ influx through voltage-sensitive (VSCC) and -insensitive Ca2+-channels (VICC) was again almost identical in PKCe–/– and wt beta-cells (Δ[Ca2+]i PKCe–/–12±1 nM (n=59) vs. Δ[Ca2+]i wt 14±1 nM (n=61, n.s). In Ca2+-free medium the carbachol (10µM)-induced Ca2+-signals were similar in PKCe–/– and in wt beta-cells demonstrating that ACH-linked mobilization was unaffected. Likewise, activation of capacitative Ca2+-influx through VICC and voltage-dependent Ca2+-influx through VSCC elicited by high K+ (45 mM) were identical in both PKCe–/– and wt beta-cells.

Conclusions: There is no evidence that PKCe, which is activated in response to ACH stimulation, could affect ACH-linked Ca2+ signalling, internal Ca2+ mobilization, Ca2+ influx through VSCC and VICC in beta-cells. The effects of PKCe on insulin release reported by others appear to occur distal to the generation of the ACH-linked calcium signal.