Do human sinoatrial node cells have t-tubules?

Every heartbeat is generated by spontaneously depolarizing specialised nodal cells that make up the sinoatrial node (SN). The SN's unique properties depend on two complex mechanisms - the membrane-voltage and the Ca2+ clocks, regulated by strictly defined expression of ion channels, connexins and Ca2+-handling proteins. In the working myocardium these proteins are accumulated in specialised membrane structures– the transverse tubules...