Role of cholesterol in developing T-tubules: Analogous mechanisms for T-tubule and caveolae biogenesis

Re cent work has suggested that caveolae biogenesis and transverse-tubule ( T-tubule) formation in muscle cells share similar underlying features. We c ompared the properties of caveolin-1 (cav-1)-positive caveolae, in epitheli al cells, with caveolin-3 (cav-1)-positive precursor T-tubules, in differen tiating C2C12 muscle cells, using the cholesterol-binding drug, Amphoterici n B (AmphB). Treatment of MDCK epithelial cells with acute high doses or ch ronic low doses of AmphB caused a loss of surface caveolae and the rapid re distribution of cav-l, and exogenously expressed cav-3, from the cell surfa ce into modified endosomes. This effect was reversible and specific, as the GPI-anchored protein, alkaline phosphatase, was largely unaffected by the treatment unless it had been previously partitioned into caveolar domains. In differentiating C2C12 mouse myotubes, AmphB also caused a complete redis tribution of cav-3 from precursor T-tubule elements into enlarged endosomes , morphologically very similar to those seen in MDCK cells. This was accomp anied by redistribution of a T-tubule marker and a dramatic reduction in th e extent of surface-connected tubular elements. We propose that cholesterol -enriched glycolipid'raft' domains are involved in the formation and mainte nance of diverse membrane systems including caveolae and the T-tubule syste m of muscle.