Page "Smooth muscle tissue" Paragraph 27

The sarcolemma also contains caveolae, which are microdomains of lipid rafts specialized to cell-signaling events and ion channels.

These invaginations in the sarcoplasma contain a host of receptors ( prostacyclin, endothelin, serotonin, muscarinic receptors, adrenergic receptors ), second messenger generators ( adenylate cyclase, Phospholipase C ), G proteins ( RhoA, G alpha ), kinases ( rho kinase-ROCK, Protein kinase C, Protein Kinase A ), ion channels ( L type Calcium channels, ATP sensitive Potassium channels, Calcium sensitive Potassium channels ) in close proximity.

The caveolae are often close to sarcoplasmic reticulum or mitochondria, and have been proposed to organize signaling molecules in the membrane.