Evidence of alpha 1-adrenergic----protein kinase C----Na+/H+ antiporter-dependent increase in pinealocyte intracellular pH. Role in the adrenergic stimulation of cGMP accumulation.

The regulation of intracellular pH (pHi) in isolated rat pinealocytes was studied using the fluorescent pH indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. Resting pHi was 7.09 when the extracellular pH (pHe) was 7.2. Treatment of pinealocytes with the physiological regulator of pineal function, norepinephrine, resulted in a concentration-dependent increase in pHi. Further analysis indicated that norepinephrine is probably acting via an alpha 1-adrenergic----[Ca2+]i----Ca2+/phospholipid- dependent protein kinase (protein kinase C) mechanism to activate the Na+/H+ antiporter, thereby causing cytoplasmic alkalization. A potential influence of cytosolic alkalization on the responsiveness of cyclic nucleotides to adrenergic agonists was also studied. Five analogs of the antiporter inhibitor amiloride reduced norepinephrine stimulation of cGMP accumulation with the same relative potency as they act on the antiporter. In contrast, although inhibitory effects of these compounds on cAMP accumulation were detectable, they occurred at 10-100-fold higher concentrations, and the relative potency of these inhibitors did not indicate they were acting via the antiporter. These findings provide evidence that 1) alpha 1-adrenergic receptor activation increases pinealocyte pHi through Ca2+----protein kinase C-dependent activation of the Na+/H+ antiporter; and 2) norepinephrine stimulation of cGMP accumulation is pHi-dependent. It would appear that alpha 1-adrenergic regulation of pHi via the Na+/H+ antiporter may be of general importance in the control of cGMP accumulation.