Figure 6. VIP elevates intracellular calcium in pinealocytes. Panels on the left compare responses of 1 mM norepinephrine (NE) and 100 nM VIP in the presence (panel A) and absence (panel B) of extracellular calcium. Panels on the right compare responses to norepinephrine and VIP in the absence (panel A) and presence (panel B) of a blocker of cyclic nucleotide-gated cation channels (l-cis-diltiazem). Studies indicate that VIP causes transient increases in calcium through a cGMP-gated cation channel (123).