Figure 2. Role of interstitial cells in regulating cavernosal smooth muscle (CSM) tone.

In corpus cavernosum, both spontaneous activity of CSM and neurally released noradrenaline (NAd; pink arrow) contract CSM. Spontaneously produced prostaglandins (PGs) via COX-2 activity in interstitial cells (ICs) not only reinforce spontaneous excitation of CSM (lower red arrow) but also facilitate nerve-mediated α-adrenergic contractions (upper red arrow). Conversely, spontaneously released nitric oxide (NO) from endothelium (EC) suppresses excitation (green arrow). Thus, the balance between spontaneously released PGs and NO is important in regulating CCSM tone to determine the contractile state of the penis.