Vascular smooth muscle cells were obtained from rabbit aorta and were studied in primary culture on days 1-7 after seeding with electrophysiological techniques. In impalement experiments a mean membrane potential difference (PD) of -50 +/- 0. 3 mV (n = 387) was obtained with Ringer-type solution in the bath. PD was depolarized by 6 +/- 0. 3 mV (n = 45) and 16 +/- 2 mV (n = 5) when the bath K+ concentration was increased from the control value of 3. 6 mmol/l to 13. 6 and 23. 6 mmol/l, respectively. Ba2+ (0. 1-1 mmol/l) depolarized PD. Tetraethylammonium (TEA, 10 mmol/l) depolarized PD only slightly but significantly. Verapamil (0. 1 mmol/l) and charybdotoxin (10 nmol/l) had no effect on PD. The conductance properties of these cells were further examined with the patch-clamp technique. K+ channels were spontaneously present in cell-attached patches. When the pipette was filled with 145 mmol/l KCl, a mean conductance (gK) of 209. 6 +/- 4. 6 mV (n = 17) was read from the current/voltage curves at a clamp voltage (Vc) of 0 mV. After excision K+ channels were found in 129 patches with inside-out and in 50 with outside-out configuration. With KCl on one and NaCl on the other side the mean gK at a Vc of 0 mV was 134. 6 +/- 3. 9 pS (n = 179). The mean permeability was 0. 89 +/- 0. 03 x 10(-12) cm3/s. With symmetrical KCl solution the mean gK was 227 +/- 6 pS (n = 17). The conductance sequence was gK much greater than gRb = gCs = gNa = 0. TEA blocked dose-dependently only from the outside (1-10 mmol/l). Lidocaine (5 mmol/l) quinidine (0. 01-1 mmol/l) and quinine (0 VSports手机版. 01-1 mmol/l) blocked from both sides. Charybdotoxin (0. 5-5 nmol/l) blocked only from the extracellular side. Ba2+ blocked from the cytosolic side and the inhibition was increased by depolarization and reduced by hyperpolarization. At a Vc of 0 mV a half-maximal inhibition (IC50) of 2 mumol/l was obtained. Verapamil and diltiazem blocked from both sides, verapamil with an IC50 of 2 mumol/l and diltiazem with an IC50 of 10 mumol/l. The open probability of this channel was increased by CA2+ on the cytosolic side at activities greater than 0. 1 mumol/l. Half-maximal activation occurred at Ca2+ activities exceeding 1 mumol/l. The present data indicate that the vascular smooth muscle cells of rabbit aorta in primary culture possess a K+ conductance. In excised patches only a maxi K+ channel was detected. This channel has properties different from the macroscopic K+ conductance. (ABSTRACT TRUNCATED AT 400 WORDS) .