Role of ANO1-Expressing PDGFRα⁺ Smooth Muscle Cells in Generating Spontaneous Phasic Contractions of the Rodent...

Spontaneous phasic contractions (SPCs) in the epididymal duct play an important role in transport and maturation of sperm. In proximal cauda of the rat epididymis, platelet-derived growth factor receptor α (PDGFRα)-positive smooth muscle cells (SMCs) generate ANO1 Ca²⁺-activated chloride channels (CaCCs)-dependent spontaneous transient inward currents (STICs) to electrically drive SPCs.

Here, we explored whether epididymal ANO1⁺, PDGFRα⁺ cells may have region-specific functions in generating SPCs.

Patch clamp technique was applied to isolated epididymal cells dispersed from the rat epididymis. Membrane potential changes and SPCs were recorded from epididymal tissue preparations using an intracellular microelectrode and video imaging, respectively. To verify ANO1 currents in PDGFRα⁺ SMCs, patch clamp recordings and immunohistochemistry were performed using PDGFRα-eGFP mice.

Rat epididymal cells of both proximal cauda and caput developed spontaneous transient depolarizations (STDs) that were inhibited by Ani9 (3 µM), the ANO1-specific inhibitor, CPA (10 µM), a sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) inhibitor, or nifedipine (1 µM), an L-type voltage-dependent Ca²⁺ channel (LVDCC) inhibitor. Ani9 (10 µM) slowed slow waves and associated SPCs in proximal cauda but not the caput. In the mouse epididymis, the proximal cauda consisted of a few layers of SMCs where SMCs in the innermost layer primarily expressed PDGFRα, whereas the caput was composed of one or two layers of PDGFRα⁺ SMCs. In both regions, Ani9 (3 µM) abolished STICs in PDGFRα⁺ SMCs that co-expressed ANO1. However, Ani9 (10 µM) slowed SPCs in the proximal cauda but not the caput.

Despite the fact that epididymal PDGFRα⁺ SMCs in both the proximal cauda and caput develop ANO1-dependent STICs, they appear to serve as pacemaker cells driving SPCs in the proximal cauda, whereas corresponding cells in the caput have a role other than SPCs' pacemaking.