Antagonists and activators at calcium channels. Effects in the gastrointestinal tract.

Most calcium antagonists have relatively minor effects in the gastrointestinal (GI) tract; the factors influencing drug selectivity are reviewed. Voltage-dependent Ca channels (VOCs) in GI smooth muscle appear to be essentially similar to those in the cardiovascular system in their sensitivity to calcium antagonists. However, selective conditions for channel activation may allow antagonists to be selective in certain disease conditions. Indirect effects on blood flow may be crucial to certain parameters (e.g., acid secretion). Activators of VOCs have similar effects in vascular and GI smooth muscle. Some endogenous activators of VOCs may exist and evidence for control of VOC activity by lipid metabolites is indicated. Acyl carnitines may function as endogenous activators of VOCs.