Intracellular applications of CaM suppressed I_ss and occluded the PMA-induced and Ca²⁺-dependent reduction ofI_ss/I_p.A, Example traces of original (top) and normalized (to peak; bottom) NMDA currents in the presence of three different [Ca²⁺]_e. Currents before (thicklines) and after (thinlines) PMA are shown with CaM (50 nm) in the patch pipettes. B, Ratios of peak-to-steady-state currents recorded with the inclusion of CaM (graycircles;n = 6) are compared with similar recordings without CaM (Control, blackcircles; the same data used in Fig.4D) and are plotted against [Ca²⁺]_e. CaM reducedI_ss/I_p in a [Ca²⁺]_e-dependent manner (0.2 mm [Ca²⁺]_e,Control, 0.55 ± 0.05; CaM, 42 ± 0.06; 1.3 mm[Ca²⁺]_e,Control, 0.53 ± 0.02; CaM, 38 ± 0.05; p < 0.05; 5.0 mm[Ca²⁺]_e,Control, 0.49 ± 0.08; CaM, 27 ± 0.06; p < 0.05). CaM enhanced the slope of theI_ss/I_p–[Ca²⁺]_erelationship from −0.012 mm⁻¹[Ca²⁺]_e in control (thinline) to −0.031 mm⁻¹ [Ca²⁺]_e(thickline). C, PMA enhanced I_p in the presence (+CaM, blackbars;n = 6) or absence (−CaM,whitebars; the same data used in Fig.4B) of CaM, and the degree of potentiation ofI_p was similar at each [Ca²⁺]_e. D, In contrast, intracellular CaM (blackbars;n = 6) enhanced the PMA-induced depression ofI_ss in the presence of low [Ca²⁺]_e, while causing no further depression in the presence of high [Ca²⁺]_e. E, With CaM in the patch pipettes,I_ss/I_precorded before (CaM,graycircles) and after (CaM + PMA,blacksquares) PMA treatment is plotted against [Ca²⁺]_e. Note that in the presence of CaM, PMA induced only a parallel shift of theI_ss/I_p–[Ca²⁺]_erelationship (−PMA, 0.031 mm⁻¹[Ca²⁺]_e; +PMA, 0.03 mm⁻¹[Ca²⁺]_e; n= 6), demonstrating that CaM occludes the Ca²⁺-dependent inactivation of these currents.