Aging increases capacitance and spontaneous transient outward current amplitude of smooth muscle cells from murine superior epigastric arteries.
Large conductance Ca(2+)-activated K(+) channels (BKCa) contribute to negative feedback regulation of smooth muscle cell (SMC) tone. However, the effects of aging on BKCa function are unclear. We tested the hypothesis that aging alters SMC BKCa function in superior epigastric arteries (SEAs) by using perforated patch recording of enzymatically isolated SMCs from 3- to 4-mo-old male C57BL/6 mice (Young) and 24- to 26-mo-old male C57BL/6 mice (Old). SMC capacitance from Young (15.7 ± 0.4 pF; n = 110) was less than Old (17.9 ± 0.5 pF; n = 104) (P < 0.05). SMCs displayed spontaneous transient outward currents (STOCs) at membrane potentials more positive than -30 mV; depolarization increased STOC amplitude and frequency (P < 0.05; n = 19-24). STOC frequency in Young (2.2 ± 0.6 Hz) was less than Old (4.2 ± 0.7 Hz) at -10 mV (P < 0.05, n = 27-30), with no difference in amplitude (1.0 ± 0.1 vs. 0.9 ± 0.1 pA/pF, respectively). At +30 mV, STOC amplitude in Young (3.2 ± 0.3 pA/pF) was less than Old (5.0 ± 0.5 pA/pF; P < 0.05, n = 61-67) with no difference in frequency (3.9 ± 0.4 vs. 3.2 ± 0.3 Hz, respectively). BKCa blockers (1 μM paxilline, 100 nM iberiotoxin, 1 mM tetraethylammonium) or a ryanodine receptor antagonist (100 μM tetracaine) inhibited STOCs (n ≥ 6; P < 0.05 each). Western blots revealed increased expression of BKCa α-subunit protein in Old. Pressure myography revealed no effect of age on SEA maximal diameter, myogenic tone, or paxilline-induced constriction (n = 10-12; P > 0.05). Enhanced functional expression of SMC BKCa-dependent STOCs in Old may represent an adaptation of resistance arteries to maintain functional integrity.
Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan;
Sebastien
S
Hayoz
College of Veterinary Medicine, Michigan State University, East Lansing, Michigan;
Vanessa
V
Bradley
Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri; and.
Erika M
EM
Boerman
Dalton Cardiovascular Research Center, Columbia, Missouri.
Zahra
Z
Nourian
Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri; and Dalton Cardiovascular Research Center, Columbia, Missouri.
Steven S
SS
Segal
Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan; jacks783@msu.edu.
William F
WF
Jackson
D000375:Aging / Q000502:physiology*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D019074:Epigastric Arteries / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology
D002121:Calcium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D019837:Ryanodine Receptor Calcium Release Channel
aging; myogenic tone; potassium channels; resistance arteries; vascular smooth muscle