BETA-ADRENERGIC REGULATION OF VOLTAGE-DEPENDENT CALCIUM CURRENTS IN CULTURED SKELETAL MYOCYTES OF THE FROG RANA-TEMPORARIA

Effects of beta-agonists isoproterenol (Isp) and adrenaline (Adr) and beta-adrenoblocker obsidan (Obs) on the voltage-dependent calcium curr ents in cultured embryonic skeletal myocytes were studied at various s tages of development ranging from day 2 to 10, using the whole-cell pa tch-clamp technique at 19-21 degrees C. Adr (or Isp) in concentrations 0.1-10 mu mol/l increases the amplitude of both the slow dihydropyrid ine(DHP)-sensitive calcium current (I-Ca) and the fast-activated DHP-i nsensitive I-Ca. From day 2 to 6 after myoblast plating, Adr and Isp d id not change the amplitude of I-Ca at all or slightly increased it. O bvious strong positive effects (an approximately twofold amplitude inc rease) on the calcium channels have been observed in 7-10-day-old myoc ytes only. beta-adrenoblocker obsidan known to abolish the positive be ta-agonist effect, had a positive effect on membrane calcium currents. It may have been a result of the immaturity of the beta-adrenergic re gulatory system of the myocytes. It is concluded that the beta-adrener gic regulatory complex can stimulate the activity of the fast and the slow voltage-dependent calcium channels of the frog skeletal myocytes, and that there is a distinct developmental stage at which a functioni ng beta-adrenergic regulatory complex appears in the membrane of skele tal myocytes.