Histochemical characteristics of bulbospongiosus and ischiocavernosus muscles in man

The histochemical profiles of the bulbospongiosus (BS) and ischiocavernosus (IC) muscles were investigated on autopsy samples obtained from 13 men aged 18 to 33. Adenosine triphosphatase (ATPase) reactions were used for differentiation of muscle fibres into type 1 (slow twitch, tonic), and type 2 (fast twitch, phasic) and subtypes 2A, 2B, 2C. The activity of oxidative and glycolytic enzymes was also assayed. Because the percentage and diameters of both fibre types varied considerably in different areas of the same muscle, two methods of counting were applied and at least two fields of each sample were evaluated. The mean percentage of type 1 fibres in BS muscles was 34.8% and 23.2%, that in IC muscles 49.7% and 39.7%. The mean diameter of type 1 fibres was 31.0 microns (BS) and 26.2 microns (IC), that of type 2 fibres ranged from 30.0 microns (BS) to 36.6 microns (IC). The comparison of BS and IC muscles with other nonskeletal voluntary muscles revealed that BS and IC muscles are similar to the striated sphincters, particularly with regard to the numerical distribution of fibre types and fibre diameters.