Multiple effects of SK&F 96365 on ionic currents and intracellular calcium in human endothelial cells

Abstract

1. 1. Multiple effects of the imidazole compound SK&F 96365 have been evaluated on endothelial cells from human umbilical vein using a combined patch clamp and Ca 2+-microfluorimetric technique (Fura-2). 2. 2. At concentrations of 100 μmol/l or higher of SK&F 96365, the block of the receptor-mediated Ca 2+ entry overlaps with the activation of another Ca 2+-entry mechanism, which is assoclated with a non selective cationic current. 3. 3. This rise in [Ca 2+] i depends on the extracellular Ca 2+-concentration, and the entry pathway is in contrast with the receptor-mediated Ca 2+-entry pathway permeable to Ni 2+, as shown by quenching of the Fura-2 fluorescence signal. 4. 4. The concentration of SK&F 96365 for half maximal increase in [Ca 2+] i was 141 ± 19 μmol/l (n = 16). 5. 5. SK&F 96365 activated a current that reversed at +11.8 ± 2.1 mV (n = 21) when measured using nystatin-perforated patches with either Cs + or K + in the pipette and 140 Na +, 1.5 Ca 2+ in the bath (chloride equillbrium potential E Cl = −36 mV). 6. 6. SK&F 96365 (200 μmol/l) blocked an inwardly rectifying K + current in endothelial cells independently of [Ca 2+] i. This block caused depolarization of the endothelial cells from −55.3 ± 2.57 mV (n = 33) to −10 ± 5.5 mV (n = 6). This block was concentration-dependent, half maximal block occurred at a concentration of about 40 μmol/l SK&F 96365. 7. 7. In cells which showed an outwardly rectifying current, this outward component was also completely blocked by 200 μmol/l SK&F 96365. 8. 8. It is concluded that SK&F 96365 reversibly activates a non-selective cation channel at concentrations higher than 100 μmol/l, but also blocks K + currents in endothelial cells independently of [Ca 2+] i. These multiple effects overlap with the proposed block of receptor-mediated Ca 2+ entry. The block of K +-channels may in unclamped cells reduce the driving force for Ca 2+, and thereby interfere with the Ca 2+-influx.