INCREASED NA+/H+ EXCHANGE ACTIVITY IN VASCULAR SMOOTH-MUSCLE CELLS OF SPONTANEOUSLY HYPERTENSIVE RATS AND POSSIBLE INVOLVEMENT OF PROTEIN-KINASE-C

1. Na+ influx into cultured vascular smooth muscle cells (VSMC) obtained from spontaneously hypertensive rats (SHR) and from Wistar-Kyoto rats (WKY) was measured. Na+ influx via the Na+/H+ exchange system was measured as the rate of Na-22(+) influx into cultured VSMC sensitive to ethylisopropylamiloride (EIPA), a specific inhibitor of the exchange system. 2. The total Na-22(+) influx rate in SHR was significantly higher than in WKY (6.08 +/- 0.16 vs 4.13 +/- 0.09 nmol/ min per mg protein; P < 0.001; n = 14). The EIPA (1 X 10(-4) mol/L)-sensitive Na-22(+) influx rate in SHR was significantly higher than that in WKY (4.32 +/- 0.27 vs 2.17 +/- 0.14 nmol/min per mg protein; P < 0.001; n = 14). There was no difference in EIPA-insensitive Na-22(+) influx between SHR and WKY. The EIPA-sensitive Na-22(+) influx rate into VSMC was significantly decreased in SHR but not in WKY by the addition of 1 X 10(-4) mol/L 1-(5-isoquinoline-sulfonyl)-methylpiperazine (H-7), an inhibitor of protein kinase C (PK-C). 3. These results suggest that the increase in Na+ influx in SHR may be due to elevation of the Na+/H+ exchange activity, and possible involvement of PK-C in the increased Na+/H+ exchange activity in VSMC from SHR.