Plasmalemmal dihydropyridine receptors modify the function of subplasmalemmal inositol 1,4,5-trisphosphate receptors: a hypothesis

Experimental observations on rat glomerulosa cells inspired a model which postulates that plasmalemmal dihydropyridine receptors are in juxtaposition and interaction with inositol 1,4,5-trisphosphate receptors in subplasmalemmal calciosomes. Activation of dihydropyridine receptors promotes the Ca²⁺ releasing effect of inositol 1,4,5-trisphosphate. The most important observations compatible with the model are the following: (1) angiotensin II does not influence Ca²⁺ influx during the peak phase of Ca²⁺ signal; (2) dihydropyridine drugs modify the initial peak of the Ca²⁺ signal induced by angiotensin II; (3) inhibitors of the dihydropyridine receptor reduce the initial Ca²⁺ signal also in the presence of 5 mM Ni²⁺, an inhibitor of voltage dependent Ca²⁺ influx; and (4) changes in extracellular K⁺ concentration within the physiological range also modify the cytoplasmic Ca²⁺ response to angiotensin II.