Key points are not available for this paper at this time.
Nexus membranes were isolated from cardiac muscles of guinea pig or ox. It was confirmed by autoradiography that Ca2+ was actually bound with the nexus, and by atomic absorption spectroscopy that bound Ca increased extensively at Ca2+ higher than 10(-6) to 10(-5) M and showed the dose-response relationship against Ca2+.
Nishiye et al. (Tue,) studied this question.