抄録
1) Effect of modified medium on tonus. The application of high concentration of Ca in medium produced an elevated tonus in SHRSP, but it did not so in WKR. This elevation in SHRSP was larger in 12M SHRSP than in 3M SHRSP. The authors reported that Ca influx was accelerated in SHRSP. These results agree with the previous report. The fact that the elevation of tonus was larger in 12M SHRSP than in 3M SHRSP suggests that the accelerated Ca influx may be more remarkable in 12M SHRSP than in 3M SHRSP. The elevation of tonus by a decrease of Na in medium was larger in SHRSP than in WKR. It was reported that the elevation of tonus by the decrease of Na might be due to Ca influx and Ca release. The fact that the elevation was found in younger SHRSP suggests that Ca influx and Ca release may be accelerated also in younger SHRSP. The fact that the elevation was larger in 12M SHRSP than in 3M SHRSP suggests that the accelerated Ca influx and Ca rlease may be more marked in 12M SHRSP than in 3M SHRSP. 2) Responses to K, NA and Ca. The responses to these contractile agents were larger in SHRSP than in WKR. The authors reported that the contractions by NA and K were due to Ca influx and Ca release. This result suggests that Ca influx and Ca release are more accel-erated in SHRSP compared with WKR. The fact that the contractions by these contractile agents were larger in 12M SHRSP than in 3M SHRSP suggests that the accelerated Ca influx and Ca release are more remarkable in 12M SHRSP than in 3M SHRSP. Immediately after the exchange to Ca-free medium, the contraction by NA was reduced in SHRSP, but that in WKR was not affected. This result suggests that the contraction by NA in SHRSP is due to Ca influx and Ca release, that in WKR being due to Ca release only. By a long time incubation in Ca-free medium, the contraction by NA disappeared in SHRSP and WKR. The disappearance time was shorter in SHRSP than in WKR. This suggests that the release of Ca from Ca store may be accelerated in SHRSP compared with WKR. The disappearance was also faster in 3M SHRSP than in 12M SHRSP. This fact suggests that the Ca content in store may be smaller in younger SHRSP than in older SHRSP
