Premium
Activation of inositol trisphosphate‐sensitive Ca2+ channels of sarcoplasmic reticulum from frog skeletal muscle.
Author(s) -
SuárezIsla B A,
Alcayaga C,
Marengo J J,
Bull R
Publication year - 1991
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1991.sp018768
Subject(s) - endoplasmic reticulum , biophysics , chemistry , skeletal muscle , inositol , ion channel , ryanodine receptor , gating , agonist , medicine , endocrinology , receptor , biochemistry , biology
1. The modulation by Ca2+ of the activation by inositol 1,4,5‐trisphosphate (IP3) of Ca2+ channels present in native sarcoplasmic reticulum membranes from frog skeletal muscle was studied after channel incorporation into planar phospholipid bilayers in the presence of Ca2+ or Ba2+ as current carrier species. 2. Channel activity expressed as fractional open time (Po) was low (less than or equal to 0.15) in the presence of varying free Ca2+ concentrations bathing the myoplasmic face of the channel (cis side), and did not increase significantly between 0.01 and 30 microM‐Ca2+. 3. Channel activation mediated by IP3 could be elicited from free Ca2+ levels similar to those of resting skeletal muscle (about 0.1 microM) and was found to be strongly regulated by the free Ca2+ concentration present at the myoplasmic moiety of the channel. 4. Channel activation by 10 microM‐IP3 depended on the Ca2+ concentration on the cis side. Po reached a maximum between pCa 7.0 and 6.0, but decreased at higher concentrations of free Ca2+. Thus, Ca2+ exerted a modulatory influence on IP3‐mediated activation in a concentration range where the channel was insensitive to Ca2+. 5. The results indicate that Ca2+ ions act as modulators of IP3 efficacy to open the channel. This could arise from an interaction of Ca2+ with the channel gating mechanism or with the agonist binding site.