Voltage-dependent calcium channels are essential for the release of neurotransmitters. L-type (long lasting current) voltage-dependent calcium channels are composed of four subunits: an Alpha1 subunit, a Beta subunit, a Beta subunit and an Alpha2 Gamma subunit. The Beta subunit is encoded by four genes, designated Beta1-Beta 4, all of which contribute to the diversity of calcium currents and are involved in membrane trafficking of the Beta subunit. L-type Ca++ CP Beta 4, also known as CACNB4 (Calcium channel voltage-dependent subunit beta 4), CACNLB4 or CAB4, is a 484 amino acid protein that contains one SH3 domain and is expressed in ovary, brain and smooth muscle. Functioning as one of the four components of the Beta subunit, L-type Ca++ CP Beta 4 increases the peak calcium current in voltage-dependent calcium channels, thereby shifting the voltage dependencies of activation and inactivation and controlling G protein inhibition and Beta membrane targeting. Two isoforms of L-type Ca++ CP Beta4 exist due to alternative splicing events.