INCREASE IN INTRACELLULAR CALCIUM IN FRESHLY-DISPERSED, SINGLE BROWN ADIPOCYTES OF THE RAT BY ADRENERGIC-STIMULATION

The concentration of cytosolic free calcium in single brown adipocytes of the rat, which were freshly dispersed with collagenase from brown adipose tissues and loaded with calcium indicator (fura-2), was contin uously measured with a fluorescence microscope and an image processor attached to a video camera. The concentration of cytosolic free calciu m showed spontaneous fluctuation of variable amplitude and frequency d epending on the site within the cell, The average concentration of the cytosolic calcium (average [Ca2+](in)) at rest was 54.1 +/- 2.0 nM (m ean +/- SE, n = 13). Noradrenaline (NA) at 10(-8) to 10(-5) R4 concent ration increased calcium concentration in a dose-dependent manner. NA was most potent at 10(-5) M increasing average [Ca2+](in) to 350.5 +/- 85.9 nM (n = 6). The effects of NA at concentrations higher than 10(- 5) M was less potent. The average [Ca2+](in) gradually increased with a latency of 0.5-2.0 min, and reached its maximum within 30 min after NA administration. Phentolamine at 10(-7) M significantly inhibited th e effect of 10(-6) M NA on [Ca2+](in), whereas propranolol at concentr ations of 10(-5) M or tower did not inhibit the effect of 10(-6) M NA. It is concluded that NA increases the calcium concentration in the br own adipocyte mainly via the alpha-adrenergic receptor and related sub cellular mechanisms.