Figure 5. Analyses of VDCC subtypes contributing to CHA-induced I_Ca inhibition.

A, a representative experiment illustrating the effect of 10⁻⁶ M CHA on I_Ca before and after application of various selective Ca²⁺ channel blockers. N-type Ca²⁺ current was the component irreversibly blocked by ω-CTx-GVIA (10⁻⁶ M; GVIA). P/Q -type Ca²⁺ current was the component irreversibly blocked by a combination of ω-Aga-IVA (10⁻⁷ M; AgaIVA) and ω-CTx-MVIIC (10⁻⁶ M; MVIIC). L-type Ca²⁺ current was the component reversibly blocked by nifedipine (10⁻⁵ M). The residual component insensitive to these drugs was regarded as R-type. B, summary of the distribution of high-voltage-activated Ca²⁺ channel subtypes (outer circle) and their fractional components which were sensitive to 10⁻⁶ M CHA (inner circle, black area) from four SON neurones. C, summary data for the relative proportion of each Ca²⁺ channel subtype that contributed to the total CHA-induced I_Ca inhibition.