COMPARISON OF K+ CHANNEL PROPERTIES IN FRESHLY ISOLATED MYOCYTES FROMTHORACIC AORTA OF WKY AND SHR

Altered function of smooth muscle cell K+ channels have been reported in hypertension, but the contribution of various K+ channel types to t hese changes has not been completely determined. The purpose of this s tudy was to compare the contribution of K+ channel types to whole cell K+ currents recorded from isolated thoracic aorta myocytes of 13 to 1 5 week old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR ). Cells were isolated by collagenase and elastase digestion, and K+ c urrents recorded using whole cell voltage clamp methods at room temper ature. Cells were superfused with a solution containing (in mmol/L) 14 0 NaCl, 5 KCl, 2 CaCl2, 1 MgCl2, 10 HEPES, and 10 glucose. Pipettes we re filled with a solution containing (in mmol/L) 120 KCl, 5 NaCl, 5 Mg ATP, 20 HEPES, and 10 BAPTA. The K+ currents (I-K) recorded from a hol ding potential (HP) of -80 mV were smaller in the SHR compared to thos e in WKY (for example, at 20 mV: WKY = 6.1 +/- 0.6 pA/pF and SHR = 3.7 +/- 0.2 pA/pF). Values of cell capacitance were not different between the two groups (WKY = 25.2 +/- 3.2 pF and SHR = 26.6 +/- 1.9 pF). A c omponent of I-K inhibited by voltage (K,) over the range from -80 to - 20 mV was smaller in SHR. The voltage dependence of K-v availability a nd activation were not significantly different between the two groups. I-K recorded from a HP = -20 mV (K-Ca) was not different between the two groups. Difference currents calculated from I-K measured at HP of -80 and -20 mV (that is, K-v) were smaller in SHR as was the fraction of I-K inhibited by 4-aminopyridine. These results suggest that under conditions of low intracellular [Ca2+] there are no differences in K-C a currents, but the K-v currents are smaller in SHR. Inhibition of K-v by 4-aminopyridine (0.1 to 10 mmol/L) caused larger increases in basa l tone in WKY aorta. These results suggest that K-v channels contribut e to resting K+ conductance in both WKY and SHR aorta, but with a rela tively larger contribution in the WKY.