Changes in free cytosolic Ca2+ in hepatocytes following alpha 1-adrenergic stimulation. Studies on Quin-2-loaded hepatocytes.

The Ca2+ selective fluorescent indicator, Quin-2, was employed to monitor continuously the concentration of free cytosolic Ca2+ Ca2+ i in isolated rat hepatocytes. Epinephrine (10(-6) M) and phenylephrine (10(-5) M), acting via alpha 1-adrenergic receptors, increases Ca2+ i from a basal concentration of approximately 0.2 microM to approximately 0.6 microM. This increase in Ca2+ i is evident as early as 1 to 1.5 s, the earliest time so far reported for any hepatic alpha 1-adrenergic event. Vasopressin (10(-8) M), after a lag which is 2 to 3 s longer, increases Ca2+ i to the same extent and at the same rate as the alpha 1-adrenergic agonists. Glucagon (10(-8) M) also increases Ca2+ i but at a significantly slower rate and only after a lag of about 10 s. All of these agents also induce an increase in the fluorescence of control cells. This Quin-2 independent fluorescence, which is due to an increased reduction of pyridine nucleotides, must be corrected for before the maximum change in Ca2+ i can be calculated but is sufficiently slow so as not to contribute to the initial rate of increase in the Quin-2-dependent fluorescence.