Free cytosolic calcium during spontaneous contractions in smooth muscle of the guinea-pig mesotubarium.
The free intracellular calcium ion concentration ([Ca2+]i) was measured simultaneously with isometric force in strips of guinea-pig mesotubarium using the Fura-2 technique. During the relaxed period (5-15 min) between spontaneous contractions [Ca2+]i continues to decrease after full mechanical relaxation to reach a minimal level of 86 +/- 8 nM (n = 9) just before the start of the next contraction. During the spontaneous contractions (5-15 min) [Ca2+]i reached a maximum of 211 +/- 19 nM and then oscillated between 155 +/- 16 nM and 194 +/- 9 nM. Increased extracellular Ca2+ concentration to 10 mM from the standard concentration of 1.5 mM caused a decreased frequency of spontaneous contractions and an increase in [Ca2+]i both in the relaxed and contracted states. In 10 mM extracellular Ca2+, addition of AlF4-, as 1 mM NaF + 10 microM AlCl3, caused a sustained increase in [Ca2+]i and maintained force. Addition of verapamil (10 microM) in this situation decreased [Ca2+]i to the resting level. The results suggest that the cyclic appearance of trains of action potentials is related to variation in [Ca2+]i, possibly via inactivation of Ca2(+)-dependent K+ channels.
Himpens
B
B
Laboratorium voor Fysiologie, Campus Gasthuisberg O/N, K.U. Leuven, Belgium.
Lydrup
M L
ML
Hellstrand
P
P
Casteels
R
R
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D005453:Fluorescence; D016257:Fura-2; D005836:Genitalia, Female / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D006168:Guinea Pigs; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D014599:Uterus / Q000737:chemistry / Q000378:metabolism / Q000502:physiology
D015221:Potassium Channels; D002118:Calcium; D016257:Fura-2