Eric Holtan just can't help himself.

Even today, nearly a decade removed from his doctoral-student days at the University of Arizona, he still considers Bruce Chamberlain, the UA's longtime director of choral activities, his teacher.

"He is always reminding me that we are colleagues, not teacher and student," Holtan said last week as he and Chamberlain prepared to join choirs for Frank Martin's Mass for Double Choir: Chamberlain's 36-voice-strong Arizona Choir of students and Holtan's professional Tucson Chamber Artists choir with 24 singers.

Collaborating is nothing new for the two, who worked together leading the Tucson Symphony Orchestra Chorus. But this is the first time they will join their respective choirs.

Which is an honor for Holtan, and a bit daunting.

"I talked to him on the phone on Monday and he said, 'Hey, can I come over to your rehearsal?' I thought 'Oh Jeez, I better really be prepared because he's my teacher. He's coming into my workshop.' It's a little intimidating," Holtan said.

"We are colleagues. He has the exact same degree as I have," Chamberlain said with a chuckle. "He is the one with the professional choir. I'm dealing with students and teaching students how to get this repertoire off the ground."

Chamberlain said he is particularly happy that they are teaming up on the Martin Double Mass.

"It is such a virtuosic piece for choir. It stretches everybody," he said.

Holtan will conduct the joint choirs in Friday's performance, and Chamberlain will take the podium Sunday.

Holtan will be at the helm for the second half of the concerts, dubbed "Brahms and Martin." TCA will perform Brahms' Liebeslieder Waltzes for chorus and piano four hands.

If you go

• What: Tucson Chamber Artists "Brahms and Martin," featuring guest artists Bruce Chamberlain and the UA's Arizona Choir.

• When, where: 8 p.m. Friday, Grace St. Paul's Episcopal Church, 2331 E. Adams St.; 3 p.m. Sunday, Catalina United Methodist Church, 2700 E. Speedway.

• Tickets: $20 and $30 in advance at www.tucsonchamberartists or $25 and $35 at the door.

• Details: 401-2651.

• Et cetera: TCA's "sneak peek" concert at 3 p.m. May 26 previews original works by Stephen Paulus the choir will record earlier in May. See website for details.