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(Hypertension. 1998;32:1060-1065.)
© 1998 American Heart Association, Inc.

Scientific Contributions

Biophysical Signals Underlying Myogenic Responses in Rat Interlobular Artery

Presented in part at the 52nd Annual Fall Conference and Scientific Sessions of the Council for High Blood Pressure Research, Philadelphia, Pa, September 15–18, 1998, and published in abstract form (Hypertension. 1998;32:616.).

Tsuneo Takenaka; Hiromichi Suzuki; Hirokazu Okada; Koichi Hayashi; Yuri Ozawa; Takao Saruta

From the Department of Medicine, Saitama Medical School, Iruma, Saitama (T.T., H.S., H.O.), and Department of Medicine, School of Medicine, Keio University, Shinjuku, Tokyo (K.H., Y.O., T.S.), Japan.

Correspondence to Takao Saruta, MD, Department of Medicine, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan.

Abstract—To assess cellular mechanisms mediating myogenic responses of interlobular artery (ILA), experiments were performed with the use of isolated perfused hydronephrotic kidneys. ILAs were divided into 3 groups according to their basal diameters: proximal (>60 µm), intermediate (40 to 60 µm), and distal (<40 µm) ILAs. Myogenic responses were obtained by stepwise increase in perfusion pressure. Greater myogenic responsiveness was observed in ILAs with smaller diameters. Diltiazem (10 µmol/L) inhibited myogenic responses of all segments of ILAs. Furthermore, gadolinium (10 µmol/L), a mechanosensitive cation channel blocker, abolished myogenic responses of distal but not proximal ILA. In contrast, 2-nitro-4-carboxyphenyl-N, N-diphenyl-carbamate (200 µmol/L), an inhibitor of phospholipase C, prevented myogenic responses of proximal but not distal ILA. Finally, basal proximal ILA diameters were increased by treatment with 50 nmol/L of staurosporine (P<0.05), and subsequent addition of thapsigargin (1 µmol/L) blocked myogenic contraction of proximal ILAs. Myogenic responses of intermediate ILAs exhibited characteristics between those of distal and proximal ILAs. Our data indicate that underlying mechanisms for myogenic responses differ in distinct segments of ILAs. The present results suggest that mechanosensitive cation channels are involved in myogenic constriction of distal ILAs. Finally, our findings provide evidence that the stimulation of phospholipase C mediates myogenic contraction of proximal ILAs.

Key Words: phospholipases • calcium • protein kinase C • membrane potential • calcium channels

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