L-type calcium channels in the axon terminal of mouse bipolar cells

Two types of calcium current (I(Ca)) have been identified in the bipolar cell of the mouse retina: a transient (T-) type current and a long lasting (L-) type current. It has been suggested that the former is present in the soma and the latter in the axon terminal. To establish the cellular localization of the two types of I(Ca), bipolar cells of the mouse retina was studied electrophysiologically in a slice preparation, and immunocytochemically by staining specific calcium channels in isolated cells. The dihydropyridine-sensitive L-type I(Ca) was recorded in the axon terminal, and the T-type current was recorded in the somatic region. Strong immunoreactivity to a polyclonal antibody against the L-type calcium channel was found in the axon terminal. These observations suggest that the L-type I(Ca) is generated at the axon terminal and contributes to the transmission of sustained depolarization.