Sodium and calcium influx induced by phorbol esters in airway smooth muscle cells

The second messenger protein kinase C (PKC) may play a critical role in the regulation of smooth muscle tone. In this study we examined how a direct stimulation of PKC in airway smooth muscle (ASM) cells influences the electrical and contractile properties of these cells. ASM preparations were obtained from adult male guinea pigs (Camm-Hartley strain). Changes in both the resting membrane potential (Em), as measured by a glass microelectrode technique, and the isometric force, measured by a copper-beryllium strain gauge, were continuously monitored. All experiments were done at the optimal length (Lmax) of ASM preparations and a temperature of 37.0 +/- 0.5 degrees C. The effects of phorbol myristate acetate (PMA), phorbol 12,13-diacetate (PDA), and 12,deoxyphorbol-13-isobutyrate (DPB) were investigated (with concentrations ranging from 10(-10) to 10(-4) M). We found that: (1) administration of all three phorbol esters caused a triphasic electrical and contractile response of ASM preparations showing initial, rapid depolarization, an increase in the isometric force, and slow hyperpolarization and relaxation of ASM followed by slow depolarization and an increase in the isometric force; (2) the presence of specific PKC inhibitor H-7 (10(-5) M) prevented development of both electrical and contractile events as induced by tested phorbols; (3) amiloride (10(-5) M) attenuated first- and second-phase responses, whereas furosemide (10(-5) M) inhibited all three responses (a sodium-free environment attenuated all three responses); (4) ouabain (10(-5) M) inhibited a second-phase response, whereas verapamil (10(-6) M) partially attenuated all three phases.(ABSTRACT TRUNCATED AT 250 WORDS)