Long-term regulation of contractility and calcium current in smooth muscle.
Longitudinal smooth muscle strips from guinea pig ileum were cultured in vitro for 5 days, and the relationship between extracellular Ca2+ and force in high-K+ medium was evaluated. In strips cultured with 10% fetal calf serum (FCS), this relationship was shifted to the right (50% effective concentration changed by 2-3 mM) compared with strips cultured without FCS. The shift was prevented by inclusion of verapamil (1 microM) during culture and mimicked by ionomycin in the absence of FCS. The intracellular Ca2+ concentration ([Ca2+]i) during stimulation with high-K+ solution or carbachol was reduced after culture with FCS, whereas the [Ca2+]i-force relationship was unaffected. Cells were isolated from cultured strips, and whole cell voltage-clamp experiments were performed. Maximum inward Ca2+ current (10 mM Ba2+), normalized to cell capacitance, was almost three times smaller in cells isolated from strips cultured with FCS. Culture with 1 microM verapamil prevented this reduction. These results suggest that increased [Ca2+]i during culture downregulates Ca2+ current density, with associated effects on contractility.
Gomez
M
M
Department of Physiology and Neuroscience, Lund University, Sweden.
Swärd
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002417:Cattle; D003470:Culture Media; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000502:physiology; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology*; D009924:Organ Culture Techniques; D011188:Potassium / Q000494:pharmacology*
D003470:Culture Media; D011188:Potassium; D002118:Calcium