PLASMA-MEMBRANE CALCIUM FLUX, PROTEIN KINASE-C ACTIVATION AND SMOOTH-MUSCLE CONTRACTION

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 235  (2) , 267-273
Abstract
Isolated perfused rabbit ear arteries contract when treated with 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of the calcium-activated, phospholipid-dependent protein kinase or C-kinase. Under conditions where the calcium concentration in the perfusate is 1.5 mM and the potassium concentration is 4.8 mM, there is a latent period of 70 .+-. 19 min (mean .+-. S.E.M., n = 10) between TPA addition and the onset of the contractile response. Once initiated, the contractile response is progressive and sustained. When perfusion conditions are altered in such a way as to modify calcium flux across the plasma membrane (i.e., raising the extracellular calcium concentration to 2.5 mM Ca++, raising the extracellular potassium concentration to 10 mM, and/or preincubating the tissues in media containing 100 nM Bay K 8644, a potent calcium channel agonist), the latency period between TPA addition and initiation of the contractile response is significantly reduced (2.5 mM Ca++, 37 .+-. 7 min; 10 mM K+ and 2.5 mM Ca++, 11 .+-. 3 min; 100 nM Bay K 8644 and 1.5 mM Ca++, 20 .+-. 7 min; 100 nM Bay K 8644 and 2.5 mM Ca2+, 8.5 .+-. 1.7 min; 10 mM K+ and 100 nM Bay K 8644, 11 .+-. 5 min). Likewise, the combination of 2.5 mM calcium, 100 nM Bay K 8644, and 3.3 .mu.M ouabain results in a contractile response 4.5 .+-. 2.0 min after TPA addition (means .+-. S.E.M., n = 4). Control tissues (absence of TPA addition) run simultaneously show no contractile responses to the various Ca++ flux regulators even after 90 min of incubation. In all treatments, the TPA-induced response, once initiated, is sustained and progressive, but rapidly and completely reversible upon addition of 25 .mu.M forskolin, an activator of adenylate cyclase. The TPA-induced response is inhibited by nitrendipine (100 nM), a dihydropyridine calcium channel antagonist.