Chemiosmotic potassium ion pump of insect epithelia

Abstract

Transporting epithelia of insects are unlike most vertebrate epithelia in that they lack a serosa and possess septate junctions. The Na+/K+ pump is absent and an electrogenic K+ uniport pump is present in such insect epithelia as lepidopteran midgut, dipteran salivary glands, and many Malpighian tubules. The K+ pump is located in the apical plasma membrane and pumps K+ out of the cells. In midgut the transepithelial K+ transport is against a potential difference (PD) in excess of 120 mV and against a 10-fold K+ concentration difference in vivo. The pump uses a K+-modulated ATPase thought to be located in particles called K+ portasomes, which resemble the F1-F0 ATPase of phosphorylating membranes. Like F1-F0 particles the K+ portasomes are located on the cation input, electronegative, ATP-binding side of the membrane and appear to pump two cations for each MgATP2- hydrolyzed. We propose that in K+-transporting epithelia and in phosphorylating membranes running backwards the portasomes orient the binding of ATP with respect to a cation-gated channel in such a way that when MgATP2- is hydrolyzed P-i is separated from MgADP-; the 2 K+ or 2 H+ ions are no longer neutralized and are repelled from the channel to the opposite side of the membrane. We have isolated the K+ portasome-containing goblet cell apical membrane from larval Manduca sexta midgut and are attempting to isolate the K+ portasomes and K+-ATPase.

Vacuolar-type proton pumps in insect epithelia

“…Moira Cioffi and Mike Wolfersberger from the Harvey laboratory were the first to explore the biochemical identity of the pump. They identified a K + -stimulated ATPase activity in partially purified plasma membranes and then in highly purified apical membranes of goblet cells (Wolfersberger et al, 1982;Harvey et al, 1983). One of us (H.W.)…”

Regulation of the V-ATPase in kidney epithelial cells: dual role in acid–base homeostasis and vesicle trafficking

“…1B) (Brown et al, 1987a). Early electron microscopy (EM) studies in insect epithelia were the first to describe these structures (Gupta and Berridge, 1966), which were later referred to as 'portasomes' (Harvey et al, 1983a;Harvey et al, 1983b). The V-ATPase bears a strong morphological resemblance to the previously described mitochondrial F 0 F 1 -ATP synthase, not surprisingly in view of the remarkable conservation of structure and subunit arrangement between these two enzymes that has occurred throughout evolution (Cross and Muller, 2004;Nelson and Nelson, 1989).…”

Cationic pathway of pH regulation in larvae ofAnopheles gambiae

“…Portasomes are especially prominent in mosquitoes (Bradley et al, 1982;Clements, 1992) (Table·2). Based on thermodynamics and cytology, Harvey et al (Harvey et al, 1983b) argued that portasomes are the equivalent of the F 1 ·sectors of ATP synthases (which can also function as F 1 -ATPases). V 1 -ATPases have been solubilized in pure form ) from isolated goblet cell apical membranes (Cioffi and Wolfersberger, 1983;Harvey, 1982) and shown beyond doubt to be portasomes (Grüber et al, 2000).…”