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.